1. Field of the Invention
This invention relates to an apparatus and method for cutting a tail from a web. More particularly, this invention relates to a tail cutting apparatus and method for cutting a tail from a web extending between a single tier dryer section to a further single tier dryer section.
2. Information Disclosure Statement
In co-pending patent application Ser. No. 014,569 filed Feb. 13, 1987, a Total BelRun dryer section is disclosed which includes a plurality of alternate top and bottom felted single tier dryer sections which alternately and successively dry alternate sides of the web as the web progresses through the dryer. Total BelRun is a Registered Trademark of Beloit Corporation.
Several advantages are presented by the aforementioned Total BelRun configuration. First, the long open draw between dryers within each dryer section is eliminated. The elimination of such open draw improves the runnability of the web. Second, the vacuum rolls between dryers maintain the sheet shrinkage restraint resulting in more uniform cross-machine directional sheet properties.
However, with the aforementioned Total BelRun configuration, a problem exists in that there is no open draw between the last dryers of the final dryer section and such an open draw is essential for the installation of a tail cutter.
Although the aforementioned problem could be overcome by the provision of a conventional two-felt dryer section in the final dryer section, such two-felted dryer section would greatly reduce the cross-directional sheet shrinkage restraint and this reduced shrinkage restraint would be in a critical portion of the drying cycle.
The present invention overcomes the aforementioned problem by providing an open draw transfer between the last two Total BelRun dryer sections and the installation of a tail cutter adjacent to such open draw transfer.
The advantages provided by the provision of a Total BelRun configuration throughout the dryer is primarily that the drying restraint is extended to the end of the dryer whereas in the conventional two-felt dryer section, the sheet tension between the dryers within a dryer section are to a large extent uncontrolled. Additionally, some web slack may develop in the area where the tail cutter is located.
However, in the configuration according to the present invention, the sheet tension in the open draw is controlled directly by adjusting the relative speeds of the final dryer section with respect to the immediate upstream dryer section.
In a conventional two-felt dryer section, the tail is generally cut just prior to the last one or two dryers. Although the sheet has nearly developed its full strength at this stage, the sheet at this point is also often very dry, particularly in dryer sections which precede a size press. The aforementioned dry sheet can be very abrasive on a cutting knife and the blade life thereof is relatively short. Typically, the knife or blade has to be replaced by a special saw which may result in dusting problems.
However, in the present invention, the web still contains enough moisture to allow a knife to be used as a tail cutter. Such knife not only inhibits the generation of sawdust but also permits the use of a simple tail cutter and minimizes the number of blade changes.
The length of the open draw in which the tail is cut on a conventional machine is often dictated by the specific dryer geometry which is required for runnability, roll and doctor mounting and for ventilation. However, in the present invention, the open draw length can be independently adjusted by adjusting the horizontal and/or vertical space between the dryers adjacent to the transfer draw. Such draw is then set to the minimum required for mounting a tail cutter. The aforementioned arrangement permits the draw length to be as short as possible.
In the present invention, in the event of sheet breakage in the last BelRun dryer section, and if such a break occurs during a tail cutting operation, the tail cutting is unaffected. This is because the sheet is unable to snap back between the dryers and the felt to reach the tail cutter knife when there are more than one or two dryers following the knife.
Therefore, it is a primary object of the present invention to provide an apparatus for cutting a tail from a web extending between a single tier dryer section to a further single tier dryer section.
Other objects and advantages of the present invention will be apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings and as defined by the appended claims.